---------------------------------------------------------- Engines-List Digest Archive --- Total Messages Posted Fri 05/30/03: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:55 AM - Engine Comparison (John Swartout) 2. 08:26 AM - Re: Engine Comparison (Tedd McHenry) 3. 09:49 AM - Re: Engine Comparison (albert piccioni) ________________________________ Message 1 _____________________________________ Time: 07:55:28 AM PST US From: "John Swartout" Subject: Engines-List: Engine Comparison --> Engines-List message posted by: "John Swartout" Can anyone explain to me why the Lycoming O-360 produces only 0.5 hp per cubic inch, while the Franklin 6A-335 B produces 0.53 hp per cubic inch-or 6% more. Both engines rated 180 hp., both normally aspirated and carbureted. The Franklin 6A-335 B is 6 cylinders, 334 cubic inch, 7:1 compression, 2800 rpm red line. The Lycoming O-360 is 4 cylinders, 361 cubic inch, 8.5:1 compression, 2700 rpm red line. The Lycoming has 8% more displacement, and the higher compression should give it at least a 5% advantage. The extra 100 rpm of the Franklin should give it-I'm guessing here-maybe 7% more hp than it would have at 2700? Seems to me the Franklin must be SIGNIFICANTLY more volumetrically efficient than the Lycoming. Any insights are appreciated. ________________________________ Message 2 _____________________________________ Time: 08:26:44 AM PST US From: Tedd McHenry Subject: Re: Engines-List: Engine Comparison --> Engines-List message posted by: Tedd McHenry John: > Seems to me the Franklin must be SIGNIFICANTLY more volumetrically > efficient than the Lycoming. These are just wild-ass guesses. The Franlin must have somewhat better volumetric efficiency than the Lycoming, I expect. But there could be other factors. While the Franklin has more cylinders, which might lead you to conclude that it has more internal friction, it also has significantly lower piston speed, because of the shorter stroke. Ring friction is probably the greatest contributor to internal friction, so the power lost to ring (and piston) friction may be significantly less in the Franklin than in a Lycoming. (The O-360 has quite a long stroke, and so high piston speeds.) Franklin doesn't state the piston rod length on their web site, but rod:stroke ratio could be a factor, too. If the Franklin's rod:stroke ratio is better, the pistons will spend more time closer to TDC on the power stroke, which improves combution efficiency. I also noticed, from the Franklin web site, that they use much more ignition advance than Lycoming. That may be because of the lower compression ratio, or because of the combustion chamber design, or both. Regardless, it will also result in more power. I don't know how old the Franklin design is, but Engine designers have learned a lot since the days when Lycomings were designed. Tedd McHenry Surrey, BC -6 wings (still) ________________________________ Message 3 _____________________________________ Time: 09:49:09 AM PST US From: "albert piccioni" Subject: Re: Engines-List: Engine Comparison --> Engines-List message posted by: "albert piccioni" you may want to personaly witness the output of the engines while they are on a dyno. a/p ----- Original Message ----- From: "John Swartout" Subject: Engines-List: Engine Comparison > --> Engines-List message posted by: "John Swartout" > > Can anyone explain to me why the Lycoming O-360 produces only 0.5 hp per > cubic inch, while the Franklin 6A-335 B produces 0.53 hp per cubic > inch-or 6% more. > > Both engines rated 180 hp., both normally aspirated and carbureted. The > Franklin 6A-335 B is 6 cylinders, 334 cubic inch, 7:1 compression, 2800 > rpm red line. The Lycoming O-360 is 4 cylinders, 361 cubic inch, 8.5:1 > compression, 2700 rpm red line. > > > The Lycoming has 8% more displacement, and the higher compression should > give it at least a 5% advantage. The extra 100 rpm of the Franklin > should give it-I'm guessing here-maybe 7% more hp than it would have at > 2700? > > > Seems to me the Franklin must be SIGNIFICANTLY more volumetrically > efficient than the Lycoming. > > > Any insights are appreciated. > >